1. Field of the Invention
The present invention relates to an image forming apparatus for printing an image onto paper, and a method for producing a printed matter.
2. Description of the Related Art
For producing a printed matter to be published or distributed, methods such as Desktop Publishing (DTP) and Print On Demand (POD) are employed. According to the methods, a predetermined image forming apparatus is used to perform printing directly based on digital image data created by using a computer instead of going through a plate-making process. As the predetermined image forming apparatus, a dedicated on-demand printer and general-purpose Office Automation (OA) equipment such as a printer or a multifunction device are used. The use of recent image forming apparatuses makes it possible to produce a printed matter having a quality comparable to that of a printed matter obtained through offset printing.
A printed matter produced with such an image forming apparatus is not limited to one having a margin (non-printed region) along the periphery of the paper surface. A printed matter is also produced whose print range to which a colored material is applied extends to the edges of the paper surface. An example of the printed matter is one that contains, as image information, an edging pattern, a background image (solid color background included), or an index for facilitating the selection of a page of a bound printed matter, for example. In general, in order to produce a printed matter of this type, an original image is first enlarged slightly on a computer by an amount of a margin to be cut. Then, the paper is cut after printing, so that an unnecessary margin part is trimmed.
The following related techniques have been proposed with respect to production of a printed matter on the assumption that the paper is cut after printing. According to one of the techniques, when images on a plurality of pages are printed onto roll paper, margins are provided between the pages (see Japanese Laid-open Patent Publication No. 2003-233480). The technique reduces the possibility that, even if a cut position is shifted within an error tolerance range, an image on the next page does not extend to an image on the current page. According to the other technique, when a plurality of images having a relatively small size such as a postcard are printed onto paper having a size larger than that of the images with the images arranged in rows and columns, amounts of the individual images extending beyond perforations which are provided on paper in advance for separation thereof are adjusted depending on the paper size (see Japanese Laid-open Patent Publication No. 2002-067424). The technique minimizes margins that are provided for reducing a direction shift of paper (skewed paper) occurring in the case of feeding paper, so that the paper surface can be used effectively.
There is a request that an image IM containing an index tag image IX of FIG. 4A is to be printed onto paper P as shown in FIG. 4B. In a state where a plurality of pieces of paper are stacked and bound, the index tag images IX are seen at the fore edge as shown in FIG. 4C, which helps a person in opening a desired page. However, ordinary image forming apparatuses are structured not to form an image in the edges of paper in order to prevent a color material, which causes a paper jam or spots, from scattering. Stated differently, paper at the time of the completion of printing has, in the edges thereof, image unformed regions where no images are formed. Since such an image unformed region is provided, a part of the index tag image IX on the paper edge side is not printed (see FIG. 5A), and, as a result, no index tag images IX are seen at the fore edge in a state where a plurality of pieces of paper are bound up (see FIG. 5B).
In order to use an image forming apparatus configured to provide image unformed regions in the edges of paper to obtain a printed matter in which an index tag image IX is seen at the fore edge, it is preferable that an image IM be printed onto paper whose region excluding the image unformed regions is larger than the image IM, and then, the paper is trimmed to remove an unnecessary part therefrom. Note, however, that a cut margin is to be secured depending on an alignment error between a cut position and a print region. A cut margin is obtained by enlarging the image IM slightly and printing the enlarged image IM in a manner similar to conventional manners. However, enlarging the image IM is not allowed in some cases. Such cases are, for example, a case in which the image IM contains a full-scale photograph as information, and a case in which the image IM contains a digital watermark in which the positional relationship of pixels is important.